Ways to Earn Money

Farming

At the start of the game, plant as many turnips as possible. At 10G per bag of seed and 210G per turnip, the profit is decent.

Once you get the harvester from Candy, look up prosperity bonus and crop price guide and plant accordingly. Get monsters to help in the farm to reduce time. Prosperity can make your earning skyrocket. (It can also make things grow too fast that you may have to spend all days harvesting). Planting a lot can earn hundreds of thousand in a harvest.

Once you can afford buying Greenifier from Lara, use it to level up crops for more income. Some people put a priority on leveling reharvestable crops first.

Cook your crops for extra money when selling

CON: complicated to set up. Especially the runeys.

PRO: get increasingly easier and more profitable over time. At one point monsters will do everything for you.

Fishing

Upgrade your rod to get higher level fish which sell for more

You can fish in any body of water around town and dungeon

The pond in the same level as the boss room in dungeons give expensive fish. Ask for a fishing day from Candy and camp at the pond all day can earn tens of thousand gold in the same day

Cook the fish for extra money

PRO: simple and quick. Good for emergency money.

CON: is pretty luck-based

Collecting

Weeds sell for 10G each

Some people cook weeds into flops to sell for 30G each

Bamboo shoots are about 100G each

Hit the trees in Mountain Road and Lake Poli with the hammer to collect fruits, sell them as are (100-300G each) or turn them into jam or juice